To provide information for the design of non-beta-lactam drugs which will bypass beta-lactam resistance mechanisms, we have begun an x-ray crystallographic study to establish the three-dimensional structure of E. coli D-alanine:D-alanine ligase, a cell wall synthesizing enzyme which is a potential drug target already well characterized biochemically and kinetically by other workers. From this D-amino acid ligase has evolved VanA, the newly-discovered enzyme responsible for an emerging enterococcal resistance to antibiotics of the vancomycin family. VanA is an altered ligase which has 45-52% sequence similarity with two DD-ligases we have crystallized. High-resolution crystallographic determination of the DD-ligase structure will therefore not only provide atomic-level information about a new target enzyme unique to bacteria, but will also provide a structure on which to build a three-dimensional model of the vancomycin resistance protein, which has so far been recalcitrant to x-ray structure analysis.